The present invention addresses a need for characterizing responses of optical systems and elements, such as liquid-based optics, to various types of vibrational loading. Vibration can negatively impact performance of optical systems used in applications such as imaging, laser pointing, and laser designation. Typically, for an imaging application, a lens or system of lenses is used with a camera system. During an exposure, where light is being collected by a camera mounted on a platform, if either the platform or an object being imaged (i.e. target) move, a resulting image may be blurred as a function of exposure time of a camera system and relative motion between platform and target. If every element in an imaging system moves together along with a stationary target, a resulting image will be clear. However, within a camera system, if there is relative motion of a lens, a camera element, or an imaging system's target, a resulting image will suffer blurring. Liquid lenses (e.g. electrowetting based liquid lenses, or pressure membrane liquid lenses, etc.) provide enhanced capability over solid lenses by the ability to change focus or tilt using voltage without conventional mechanical elements. Despite this advantage, liquid lenses can suffer from undesirable effects due to vibration such as resonant modes at frequencies dependent on geometrical and material properties. One approach to reducing such undesirable responses to vibration is to reduce the size of a liquid lens. However, light collection and imaging capabilities are reduced as size of the optical element (i.e. aperture) is reduced, thus limiting ability to use such lenses. When comparing image quality produced through an optical element (e.g. a glass, plastic, or a liquid lens system), there can be issues differentiating between blur caused by external vibrations of base equipment and blur caused by structural bending or displacement of optical elements (e.g. bending resonance mode in a glass lens, or shifting of liquids within a liquid lens). Typically in some cases (e.g. for liquid lenses), an assumption can be made that surface tension is much higher than any sort of vibration effects, so any deformation, and thus degradation in optical performance, caused by vibrations can be neglected. However, no capability exists that characterizes vibration effects for optical systems that may be sensitive to vibration (e.g. liquid lenses). Thus, a need exists to determine if a particular optical imaging system design will function in a particular end application or environment relative to expected vibrational loading associated with that application or environment.
Systems and related methods are provided to perform optical characterization of system under tests (SUT), including one or more optical elements (OE), for various purposes including evaluation of optical resolution needed to distinguish image elements, blur, line of sight jitter, and/or pointing stability. Various testing systems and methods are provided including an embodiment having a vibration loading system (VLS), a first acceleration sensor coupled with the VLS, and a mounting structure adapted to receive the SUT. An illumination target system (ITS) emits light that passes through the SUT OE's lens and is captured by the SUT's imaging system. A light control system controls the ITS based on a plurality of activation commands and a Test Control System (TCS). The TCS receives ITS input through the SUT that is synchronized with acceleration sensor data (e.g. phase of VLS position) and analyzed via real-time or post processing.
One type or example of post processing can include modulation transfer function (MTF) processing which generally can include embodiments to measures optical resolution as a function of vibration frequency which can be used to determine performance of optical elements during vibration loading, e.g. blur. An additional post-processing approach can include distortion mapping, which allows analysis of vibration induced geometric aberrations as represented in a data image. For example, if a set of equally spaced dots forming a grid pattern were imaged and no distortion were present, the recorded image would also be equally spaced dots forming a grid pattern. If distortion were present, however, the exemplary recorded image would have non-equally spaced dots that form an alternative pattern that can be measured and quantified to form a mapping from the original equal spacing to the alternative pattern. This exemplary measurement method can be used to determine whether structural displacement in an optical element causes optical performance issues. This additional exemplary post-processing approach can be used separately or in addition to other post processing including MTF post processing.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.